High quality fuels can be produced by catalytic alkylation of hydrocarbons. In such a process an olefin and an isoparaffin are reacted in the presence of a hydrogen fluoride catalyst to produce an alkylate. In order to further improve the octane number of such alkylates, it has been found in recent years (e.g. U.S. Pat. No. 3,842,140) that ethyl fluoride can be advantageously employed in addition to the hydrogen fluoride in the alkylation reaction. During the alkylation a certain quantity of propane is withdrawn from the alkylation reaction zone together with the alkylate and, since propane and ethyl fluoride have very similar boiling points, a certain quantity of ethyl fluoride is admixed in the propane vapor leaving the depropanizing zone of an alkylation unit. Since the ethyl fluoride content of the propane is detrimental to the use thereof as a fuel, it has been proposed to extract the ethyl fluoride from propane by contacting the propane vapor stream containing ethyl fluoride with a liquid HF stream.
One of the problems arising in this process is that the mixture of ethyl fluoride and hydrogen fluoride produced by this extraction does not have a composition that allows a recycling of this mixture to the hydrogen fluoride alkylation unit. Therefore, it is necessary to separate the two components first. Furthermore, in some alkylation plants ethylene is not readily available. In such plants ethyl fluoride could, therefore, be used directly as an additive as explained to improve the octane number of the alkylate. Therefore, it would be desirable to have a process available in which relatively pure ethyl fluoride is produced that then could be used for the alkylation process.